This invention relates generally to ballasts with thermal protection, and more specifically to thermal protector mounting devices.
Electrical lighting fixtures often involve the use of ballasts, and it is known practice to provide protection from overheating by including thermal protectors in the circuitry in order to break the flow of current to the ballasts when the thermal protector reaches a predetermined temperature. The prior art includes a variety of mounting devices for securing thermal protectors in relationship with ballasts and other electrical devices.
Among the factors which contribute to the performance and cost of providing thermal protection are the following: (1) how well and how reliably the thermal protector is held in contact with the device being protected; (2) the heat transfer from the ballast to the thermal protector itself; (3) the cost of material and fabrication of the mounting means; and (4) the cost of assembly and installation. There is a need for very low cost and easily usable devices to hold thermal protectors in place and to ensure that good thermal contact is established and held between thermal protectors and the devices being protected, particularly ballasts such as those used in lighting fixtures.
Typically, a ballast has two leads for the secondary (output) side of the ballast but provides more than two leads as connections to the primary (input) coils, allowing a manufacturer to use common parts for a variety of end usage voltages (e.g., 120V, 208V, 240V, 277V and 480V) or allowing an installer the flexibility to use the same ballast for a variety of different input voltages. However, providing such flexibility translates into higher assembly or installation costs for the electrical lighting manufacturer or installer, and, in both cases, creates opportunities for assembly or installation errors.
Some of the prior art involving securing thermal protectors with respect to electrical devices such as ballasts include the following United States patents: U.S. Pat. No. 4,861,943 (Yarmark); U.S. Pat. No. 5,126,510 (Bauer et al.); U.S. Pat. No. 5,463,522 (van Wagener et al.); U.S. Pat No. 4,924,350 (Reddy et al.); and U.S. Pat. No. 5,926,659 (Matsui). These prior disclosures fall short of offering and delivering simple, effective devices for mounting thermal protectors to electrical devices such as ballasts for lighting fixtures.
There is a need for an improved thermal protector mounting device which combines a number of advantages and features including: holding the thermal protector directly against the surface of the ballast; doing so with a simple, one-piece structure which easily and reliably places the thermal protector in predictable heat transfer relationship with the electrical device such as a ballast; and providing simplicity of assembly, installation and thermal protector replacement when needed, all at minimum cost.
Accordingly, it is a principal object of this invention to provide a low-cost bracket to mount thermal protectors to electrical devices such as ballasts for lighting fixtures.
Another object of this invention is to provide a mounting bracket which enables a thermal protector to be in direct contact with the ballast or other electrical device being protected.
Yet another object of this invention is to provide an improved ballast with thermal protection that is assembled with its thermal protector in a manufacturing plant, independent of which primary leads of the ballast are required by the input voltage of the particular lighting applicationsxe2x80x94rather than being wired in during installation into a particular lighting fixture.
Another object of the invention is to provide a bracket for mounting a thermal protector which prevents the thermal protector from being dislodged easily from the mounting bracket.
Another object of the invention is to provide a bracket for mounting a thermal protector which enables the thermal protector to be replaced easily.
Yet another object of this invention is to minimize the cost of assembly and installation of thermal protectors into electrical systems such as lighting fixtures.
Another object of the invention is to provide a bracket for mounting a thermal protector which prevents damage to the wires of the thermal protector.
These and other objects of the invention will be apparent from the following descriptions and from the drawings.
The present invention is an improved mounting bracket for thermal protectors for use on electrical devices such as ballasts which overcomes the above-noted problems and shortcomings and satisfies the objects of the invention. The invention also involves improved thermally-protected ballasts including such brackets.
In describing the invention, certain terminology is used which is defined as follows: The term xe2x80x9cunitaryxe2x80x9d as used herein refers to the fact that the mounting bracket is made of a single piece of material; e.g., in a highly preferred embodiment the bracket is a single piece stamped from spring steel sheet stock. The term xe2x80x9cholding-face portionxe2x80x9d as used herein refers to the portion of the inventive bracket through which, as hereafter described, the bracket pushes the thermal protector into reliable direct contact with the ballast or other electrical device.
The unitary bracket of this invention is used for mounting a thermal protector to an electrical device such as a ballast for lighting fixtures. The inventive bracket includes: (1) a holding-face portion having therealong opposite edges and a mounting end; (2) edge portions on the opposite edges of the holding-face portion and angled with respect thereto toward the electrical device; and (3) a mounting-end portion on the mounting end and extending toward the electrical device, the mounting-end portion having a mounting tab for engagement with the electrical device, the portions being configured and dimensioned to sandwich the thermal protector against the electrical device when the mounting-end portion is secured thereto.
In a particular embodiment of the invention, the thermal protector has a contact side for contact with a contact surface of the electrical device and a thickness dimension extending from the contact side, and the mounting-end portion is configured and dimensioned such that, with the thermal protector removed, the holding-face portion is positioned no farther from the contact surface of the electrical device than the thickness dimension of the thermal protector. In a further embodiment of the unitary bracket, with the thermal protector removed, the holding-face portion is positioned slightly closer to the contact surface of the electrical device than the thickness dimension of the thermal protector.
In some preferred embodiments of the unitary bracket, the unitary bracket is of a springy material, and in particular embodiments, the springy material is a springy metal such as spring steel.
In preferred embodiments of the inventive bracket, the edge portions and the holding-face portion of the unitary bracket together form an opening for insertion of the thermal protector and from which wires of the thermal protector extend, thereby facilitating assembly and replacement. It is preferred that the unitary bracket include a finger-tab portion on the holding-face portion at the insertion opening, the finger-tab portion extending part way toward the electrical device and having a smooth surface facing the electrical device for finger and wire contact. It is also preferred that the bracket include a retention spur projecting from the holding-face portion near the insertion opening in position to prevent unintended withdrawal of the thermal protector.
The thermal protector has a contact side for contact with a contact surface of the ballast or other electrical device and a thickness dimension extending from the contact side. One particularly preferred embodiment involves: the ballast or other electrical device having an adjacent surface which is adjacent to the contact surface; the edge portions of the unitary bracket being parallel to one another; and one of the edge portions (a wider portion) extending from the holding-face portion of the bracket to a distal edge which is farther from the holding-face portion than the thickness dimension of the thermal protector. In this preferred configuration, such wider edge portion serves an alignment function to properly position the thermal protector on the contact surface of the electrical device. More specifically, the wider edge portion engages the adjacent surface of the ballast or other electrical device, and thus facilitates the desired engagement of the contact side of the thermal protector with the contact surface of the ballast or other electrical device.
In preferred embodiments, as already noted, the electrical device with which the mounting bracket is used is a ballast for electrical lighting fixtures, the ballast being of the type having thermal protection. Each such ballast has ballast laminations and primary and secondary coils, a thermal protector and a mounting device for securing the thermal protector to the ballast.
In highly preferred embodiments, the mounting tab of the unitary bracket has a hole therethrough and is secured to the ballast with a fastener. In certain highly preferred embodiments, the ballast is of the type having its laminations held together by at least one ballast bolt therethrough and the fastener is one of the ballast bolts. In certain preferred embodiments, the thermal protector of the improved ballast is wired in series with the secondary coil of the ballast. This electrical configuration enables wiring assembly of the thermal protector with the ballast to be independent of the input voltage to the primary coil required by the particular usage of the ballast, thereby significantly simplifying assembly and installation, lowering cost and eliminating wiring errors.